In small saucepan, combine cocoa, sugar and cornstarch. Whisk in milk until blended, then corn syrup and vanilla. Bring to boil over medium-high heat, whisking constantly, reduce heat to low and cook, whisking for 1 to 2 minutes or till thickened and glossy. Let cool for 5 minutes. Spread evenly over cake. Sprinkle with glitter if desired.